C中的双三次插值 [英] Bicubic interpolation in C
问题描述
im试图处理c中的立方体图像插值.因此，我已经构建了这个小脚本.
im trying to deal with the bicubic image interpolation in c. Therefore i've built this small script.
1. "resize_image"功能:
void resize_image(PPMImage *source_image, PPMImage *destination_image, float scale) {
uint8_t sample[3];
int y, x;
destination_image->x = (long)((float)(source_image->x)*scale);
destination_image->y = (long)((float)(source_image->y)*scale);
for (y = 0; y < destination_image->y; y++) {
float v = (float)y / (float)(destination_image->y - 1);
for (x = 0; x < destination_image->x; ++x) {
float u = (float)x / (float)(destination_image->x - 1);
sample_bicubic(source_image, u, v, sample);
destination_image->data[x+((destination_image->y)*y)].red = sample[0];
destination_image->data[x+((destination_image->y)*y)].green = sample[1];
destination_image->data[x+((destination_image->y)*y)].blue = sample[2];
}
}
}
2. "sample_bicubic"功能
void sample_bicubic(PPMImage *source_image, float u, float v, uint8_t sample[]) {
float x = (u * source_image->x)-0.5;
int xint = (int)x;
float xfract = x-floor(x);
float y = (v * source_image->y) - 0.5;
int yint = (int)y;
float yfract = y - floor(y);
int i;
uint8_t p00[3];
uint8_t p10[3];
uint8_t p20[3];
uint8_t p30[3];
uint8_t p01[3];
uint8_t p11[3];
uint8_t p21[3];
uint8_t p31[3];
uint8_t p02[3];
uint8_t p12[3];
uint8_t p22[3];
uint8_t p32[3];
uint8_t p03[3];
uint8_t p13[3];
uint8_t p23[3];
uint8_t p33[3];
// 1st row
get_pixel_clamped(source_image, xint - 1, yint - 1, p00);
get_pixel_clamped(source_image, xint + 0, yint - 1, p10);
get_pixel_clamped(source_image, xint + 1, yint - 1, p20);
get_pixel_clamped(source_image, xint + 2, yint - 1, p30);
// 2nd row
get_pixel_clamped(source_image, xint - 1, yint + 0, p01);
get_pixel_clamped(source_image, xint + 0, yint + 0, p11);
get_pixel_clamped(source_image, xint + 1, yint + 0, p21);
get_pixel_clamped(source_image, xint + 2, yint + 0, p31);
// 3rd row
get_pixel_clamped(source_image, xint - 1, yint + 1, p02);
get_pixel_clamped(source_image, xint + 0, yint + 1, p12);
get_pixel_clamped(source_image, xint + 1, yint + 1, p22);
get_pixel_clamped(source_image, xint + 2, yint + 1, p32);
// 4th row
get_pixel_clamped(source_image, xint - 1, yint + 2, p03);
get_pixel_clamped(source_image, xint + 0, yint + 2, p13);
get_pixel_clamped(source_image, xint + 1, yint + 2, p23);
get_pixel_clamped(source_image, xint + 2, yint + 2, p33);
// interpolate bi-cubically!
for (i = 0; i < 3; i++) {
float col0 = cubic_hermite(p00[i], p10[i], p20[i], p30[i], xfract);
float col1 = cubic_hermite(p01[i], p11[i], p21[i], p31[i], xfract);
float col2 = cubic_hermite(p02[i], p12[i], p22[i], p32[i], xfract);
float col3 = cubic_hermite(p03[i], p13[i], p23[i], p33[i], xfract);
float value = cubic_hermite(col0, col1, col2, col3, yfract);
CLAMP(value, 0.0f, 255.0f);
sample[i] = (uint8_t)value;
printf("sample[%d]=%d\n",i,sample[i]);
}
}
3. 插补助手"
float cubic_hermite(float A, float B, float C, float D, float t) {
float a = -A / 2.0f + (3.0f*B) / 2.0f - (3.0f*C) / 2.0f + D / 2.0f;
float b = A - (5.0f*B) / 2.0f + 2.0f*C - D / 2.0f;
float c = -A / 2.0f + C / 2.0f;
float d = B;
return a*t*t*t + b*t*t + c*t + d;
}
void get_pixel_clamped(PPMImage *source_image, int x, int y, uint8_t temp[]) {
CLAMP(x, 0, source_image->x - 1);
CLAMP(y, 0, source_image->y - 1);
temp[0] = source_image->data[x+(W*y)].red;
temp[1] = source_image->data[x+(W*y)].green;
temp[2] = source_image->data[x+(W*y)].blue;
}
我已经在此处上上传了完整的代码以及所有内容.
I've uploaded the complete code with all the stuff around here.
执行此代码没有语法错误.
但是输出图像使我感到困惑.
But the output image confused me.
输入图像(21x20Pixel):
此输入图像放大2(42x40Pixel):
插值在某些点上似乎可以正常工作，但是图像看起来像是在移动像素.
The interpolation seems to work fine at some points, but the image looks like pixels are shifted.
有人可以告诉我我在做什么错吗? 该脚本是在以下帮助下制作的: http://blog.demofox.org/2015 15年8月15日/带有双曲线插值的调整大小图像/
Can someone tell me what i'm doing wrong? This script was made with the help of: http://blog.demofox.org/2015/08/15/resizing-images-with-bicubic-interpolation/
谢谢大家！
(请不要考虑这段代码的效率...我知道这太棒了)
(Please don't consider the efficiency of this code ... its aweful i know)
推荐答案
通过您的resize_image()函数:
From your resize_image() function:
destination_image->data[x+((destination_image->y)*y)].red = sample[0];
应该是
destination_image->data[x+((destination_image->x)*y)].red = sample[0];
有助于调试此类情况的方法是使用一些实际颜色中没有的魔术色"来初始化目标图像(例如，一些可怕的粉红色:-).然后您可能会注意到，在resize_image()调用之后，某些目标像素仍然具有该颜色.这暗示了这个问题.
What helps debugging such cases is initializing your destination image with some "magic color" that's not present in your actual data (e.g. some awful pink:-)). Then you would probably notice that some destination pixels still have that color after the resize_image() call. This hints to the problem.
这篇关于C中的双三次插值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
